Switchmode power supplies often employ a drive circuit to couple large FET or MOSFET transistors to a high frequency pulse transformer. In such circumstances, it is typically necessary to swing the FET or MOSFET gate voltage over a relatively large range (such as from +15V to -15V) in order to reset the core flux of the transformer. This voltage swing requirement has caused problems in prior art drive circuits.
For example, prior art drive circuits which require large gate voltage swings are disadvantageous in that they waste energy unnecessarily driving the gate of the FET or MOSFET to a negative level and subsequently returning the gate to an appropriate positive level for the next turn-on. Some such prior art drive circuits are also disadvantaged in that they require excessive turn-off time for the driven FET or MOSFET, and/or they provide excessively hard (i.e., rapid) turn-on of the driven FET or MOSFET.